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"Fast Chemical-Shift T1 Imaging
in Toroid Cavities for the Structural Analysis of Gels and Emulsions"
P. Trautner and K. Woelk, Appl.
Magn. Reson. 22, 291-305 (2002).
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Fast chemical-shift T1 imaging in toroid cavity cells
(TCCs) is introduced, and applications to diagnostic ultrasound gel and
skin-care ointment are presented.
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TCCs are an advancement over previously used toroid cavity detectors because
they combine resonator and sample container into one part. Additionally,
they are removable from the top of the probe and facilitate convenient
probe and sample handling.
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Radially resolved T1 relaxation times in TCCs are obtained
through combination of SR (saturation recovery) experiments with the RIPT
(rapid imaging with a pulse train) technique. Because of the strong radial
B1
gradient in TCCs, only pulse-burst saturation was found satisfactory to
generate the most even starting condition for SR experiments.
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Because RIPT does not resolve chemical-shift information, magnetization
and T1 profiles of individual components in mixed samples
are monitored by double-transient experiments with selective on-resonance
saturation, which is achieved by converging trains of sinc pulses.
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The new techniques were applied to cellulose hydrogel and oil-in-water
(O/W) emulsion both exposed to significant shear stress deformation during
the charging of the TCC. In both cases, T1 profiles as
a function of time reveal structural recovery (thixotropy) that slowly
progresses from one or more sample interfaces into the bulk.
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K. Woelk, October
1, 2002